It has been reported that the reactivity and selectivity of transition-metal catalysts can be modulated by the choice of ligands such as phosphorus and N-heterocyclic carbene ligands. Thus, the ligand design is one of major topics in transition metal catalysis. For that purpose, we recently reported bicyclic bridgehead phosphoramidites (briphos) as a new type of π-acceptor ligand.1 Compared with their linear analogues such as monophos, briphos ligands show enhanced π-acceptor ability induced by geometrical constraints. In addition, briphos allows for facile steric and electronic tuning because of their simple and practical synthetic procedures. Here, we explored Pd-catalyzed allylations by using briphos ligands.
Pd-catalyzed allylic substitution with allyl alcohols is attractive because only a stoichiometric amount of water can be produced as a by-product. However, the utilization of allyl alcohols is only limited to good nucleophiles such as malonates, alkyl amines, and anilines.2 Moreover, Pd-catalyzed substitution reactions of allylic alcohols with poor nucleophiles such as imidazoles and benzimidazoles are rarely reported.3 Herein, we report an efficient Pd-catalyzed allylation of allyl alcohols with a variety of N-heterocycles facilitated by a π-acceptor ligand, briphos, in a tandem catalytic cycle.
1. H. Kim, W. Y. Kim, A. Lee, S. Ahn and K. Kang, Org. Lett. 2014, 16, 5490.
2. T. Ikariya, Y. Kayaki and T. Koda, J. Org. Chem. 2004, 69, 2595.
3. M. Beller, D. Banerjee, R. V. Jagadeesh, K. Junge and H. Junge, Angew. Chem. Int. Ed. 2012, 51, 11556.